Trypsin and N-aminopeptidase (APN) activities in the hepatopancreas of an intertidal euryhaline crab: Biochemical characteristics and differential modulation by histamine and salinity.

No studies are available about biochemical characteristics and modulation (i.e. by endogenous and/or environmental cues) of trypsin (a key digestive endoprotease) in hepatopancreas of intertidal euryhaline crabs neither on the possible concomitant modulation of key ectoproteases such as aminopeptidase-N (APN) involved in final steps of protein digestion. Furthermore, nothing is still known in decapods crustaceans about the role of histamine as primary chemical messenger for modulation of main components of digestive process (i.e. proteases). We determined biochemical characteristics and investigated the effect of histamine injections; of histamine in vitro and of acclimation of individuals to low and high salinity on trypsin and aminopeptidase-N (APN) activities in the hepatopancreas of the euryhaline crab Cyrtograpsus angulatus (Dana 1851). Trypsin activity was maximal at pH7.4 and at 45°C. APN activity increased from pH6.6 to 7.6-9.0 and was maintained high at 37-45°C. Both activities exhibited Michaelis-Menten kinetics (apparent Km: trypsin=0.36mM; APN=0.07mM). The injection of 10-4M histamine decreased trypsin activity (about 40%) in hepatopancreas while did not affect APN activity. Similarly, in vitro 10-4M histamine decreased trypsin activity (about 52%) in hepatopancreas but not APN activity. Trypsin activity in the hepatopancreas was not affected by acclimation of crabs to low (10psu) or high (40psu) environmental salinity while APN activity was increased (about 200%) in 10psu. The results show the differential modulation of trypsin and APN by distinct cues and point to histamine as modulator of intracellular trypsin by direct action on the hepatopancreas.

Glucose homeostasis in the euryhaline crab Cytograpsus angulatus: Effects of the salinity in the amylase, maltase and sucrase activities in the hepatopancreas and in the carbohydrate reserves in different tissues.

We studied the existence, biochemical characteristics and response to different environmental salinities of amylase, maltase and sucrase activity in the intertidal euryhaline crab Cyrtograpsus angulatus (Dana, 1852) along with the response to distinct salinities of glycogen and free glucose content in storage organs. Amylase, maltase and sucrase activities were kept over a broad range of pH and temperature and exhibited Michaelis-Menten kinetics. Zymography showed the existence of two amylase forms in crabs exposed to 35 (osmoconformation) and low (6-10psu; hyper-regulation) or high (40psu) (hypo-regulation) salinities. Carbohydrases activity in the hepatopancreas and glycemia were not affected in crab exposed to different environmental salinities. In 6 and 40psu, the glycogen content in anterior gills was lower than in 35psu. In 6, 10 and 40psu, glycogen concentration in hepatopancreas, muscle and posterior gills were similar to that in 35psu. Free glucose concentration in chela muscle was higher in 6 and 40psu than in 35psu. The existence and biochemical characteristics of carbohydrases activity and the adjustments in concentration of glycogen in anterior gills and free glucose in chela muscle suggests the ability to perform complete hydrolysis of glycogenic substrates and to keep glucose homeostasis in relation to acclimation to different salinity conditions.